U.S. patent application number 14/495901 was filed with the patent office on 2015-04-02 for flux for soldering and solder paste composition.
This patent application is currently assigned to TAMURA CORPORATION. The applicant listed for this patent is TAMURA CORPORATION. Invention is credited to Masaya ARAI, Akira KITAMURA, Momoko SEINO, Masahiro TSUCHIYA.
Application Number | 20150090367 14/495901 |
Document ID | / |
Family ID | 52738927 |
Filed Date | 2015-04-02 |
United States Patent
Application |
20150090367 |
Kind Code |
A1 |
TSUCHIYA; Masahiro ; et
al. |
April 2, 2015 |
FLUX FOR SOLDERING AND SOLDER PASTE COMPOSITION
Abstract
A flux for soldering includes a base resin, a solvent, and an
activating agent. The base resin contains a rosin. An amount of the
rosin to be incorporated is from 0% by weight to 30% by weight with
respect to a total amount of the base resin. The activating agent
includes a compound having a plurality of carboxyl groups on a
cyclohexyl structure represented by a general formula (1).
##STR00001## X is (a) one or more carboxyl groups, or (b) one or
more carboxyl groups and at least one selected from a hydrogen
atom, chloro group, bromo group, alkyl group, and cyclohexyl group.
A position of the X is not limited. A number of the X is one or
more. The X may have either one of the (a) and (b) alone, or a
plurality of the (a) and (b) in combination.
Inventors: |
TSUCHIYA; Masahiro;
(Iruma-shi, JP) ; KITAMURA; Akira; (Iruma-shi,
JP) ; SEINO; Momoko; (Iruma-shi, JP) ; ARAI;
Masaya; (Iruma-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TAMURA CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
TAMURA CORPORATION
Tokyo
JP
|
Family ID: |
52738927 |
Appl. No.: |
14/495901 |
Filed: |
September 25, 2014 |
Current U.S.
Class: |
148/24 ;
148/23 |
Current CPC
Class: |
B23K 35/3612 20130101;
B23K 35/025 20130101; B23K 35/362 20130101 |
Class at
Publication: |
148/24 ;
148/23 |
International
Class: |
B23K 35/36 20060101
B23K035/36; B23K 35/362 20060101 B23K035/362; B23K 35/02 20060101
B23K035/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2013 |
JP |
2013-203069 |
Claims
1. A flux for soldering, comprising: a base resin containing a
rosin, an amount of the rosin to be incorporated being from 0% by
weight to 30% by weight with respect to a total amount of the base
resin; a solvent; and an activating agent including a compound
having a plurality of carboxyl groups on a cyclohexyl structure
represented by a general formula (1) ##STR00007## wherein X is (a)
one or more carboxyl groups, or (b) one or more carboxyl groups and
at least one selected from a hydrogen atom, chloro group, bromo
group, alkyl group, and cyclohexyl group, a position of the X is
not limited, a number of the X is one or more, and the X may have
either one of the (a) and (b) alone, or a plurality of the (a) and
(b) in combination.
2. The flux for soldering according to claim 1, wherein an amount
of the compound to be incorporated having a plurality of carboxyl
groups on a cyclohexyl structure represented by the general formula
(1) is of 0.5% by weight or more with respect to a total amount of
the flux for soldering.
3. The flux for soldering according to claim 1, wherein the
compound having a plurality of carboxyl groups on a cyclohexyl
structure represented by the general formula (1) is at least one of
cyclohexanedicarboxylic acid, hydrogenated trimellitic acid, and
hydrogenated pyromellitic acid.
4. The flux for soldering according to claim 1, wherein an amount
of the base resin to be incorporated is from 30% by weight to 60%
by weight with respect to a total amount of the flux for soldering,
an amount of the activating agent to be incorporated is from 5% by
weight to 15% by weight with respect to the total amount of the
flux for soldering, an amount of the solvent to be incorporated is
from 20% by weight to 50% by weight with respect to the total
amount of the flux for soldering, the amount of the rosin to be
incorporated is from 0% by weight to 30% by weight with respect to
the total amount of the base resin, and an amount of the compound
to be incorporated having a plurality of carboxyl groups on a
cyclohexyl structure represented by the general formula (1) is of
0.5% by weight or more with respect to the total amount of the flux
for soldering.
5. A solder paste composition, comprising: a solder alloy powder;
and a flux for soldering, comprising: a base resin containing a
rosin, an amount of the rosin to be incorporated being from 0% by
weight to 30% by weight with respect to a total amount of the base
resin; a solvent; and an activating agent including a compound
having a plurality of carboxyl groups on a cyclohexyl structure
represented by a general formula (1) ##STR00008## wherein X is (a)
one or more carboxyl groups, or (b) one or more carboxyl groups and
at least one selected from a hydrogen atom, chloro group, bromo
group, alkyl group, and cyclohexyl group, a position of the X is
not limited, a number of the X is one or more, and the X may have
either one of the (a) and (b) alone, or a plurality of the (a) and
(b) in combination.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority under 35 U.S.C.
.sctn.119 to Japanese Patent Application No. 2013-203069, filed
Sep. 30, 2013. The contents of this application are incorporated
herein by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a flux for soldering and a
solder paste composition.
[0004] 2. Description of the Related Art
[0005] A solder paste composition used in mounting an electronic
component on a board is prepared by mixing a flux for soldering and
a solder alloy powder. When soldering is done with the use of this
solder paste composition, a part of the flux for soldering tends to
remain in the vicinity of a solder-jointed part on a board as a
flux residue.
[0006] In general, the above mentioned flux for soldering contains
a base resin, an activating agent and a solvent. In addition, as
this base resin, a rosin is widely used conventionally.
[0007] In accordance with the recent higher performance,
densification or the like of an electronics product, situations are
increasing where a board is exposed to an environment having
drastic changes in temperature. Under such an environment, a flux
residue that is formed by using a flux for soldering, in which a
rosin is used as a base resin, is easy to become hard and fragile,
due to its inherent nature. Furthermore, the above mentioned flux
residue becomes easy to crack with time. Accordingly, through the
crack, water becomes easy to infiltrate a circuit part of a board,
thereby creating problems including the short-circuit of a circuit
and the metal corrosion of the circuit.
[0008] As a method for solving the above mentioned problems, there
is a method for preventing the flux residue from remaining on a
board at the completion of soldering, without incorporating any
rosin into a flux for soldering, as disclosed in, for example, JP
2006-289497 A. In addition, there is a method in which another
resin instead of a rosin is used as a base resin, or a rosin and
another resin are used together, as disclosed in, for example, JP
2011-121059.
[0009] However, even when such a flux for soldering disclosed in JP
2006-289497 A mentioned above is used, it is difficult to
completely eliminate the flux residue. In addition, a solder paste
composition, in which a flux for soldering with the rosin content
reduced is used, reduces the reflow property. Accordingly, it is
necessary to increase the content of an activating agent for such a
solder paste composition, which may disturb the printability of the
solder paste composition.
[0010] In addition, a flux for a solder paste disclosed in JP
2011-121059 A mentioned above needs to incorporate a given amount
of rosins, for the purpose of improving the printability of a
solder paste composition. Accordingly, the flux residue that is
formed by using such a solder paste composition causes uncertainty
involving the crack initiation or development under an environment
having drastic changes in temperature.
SUMMARY OF THE INVENTION
[0011] According to one aspect of the present invention, a flux for
soldering includes a base resin, a solvent, and an activating
agent. The base resin contains a rosin. An amount of the rosin to
be incorporated is from 0% by weight to 30% by weight with respect
to a total amount of the base resin. The activating agent includes
a compound having a plurality of carboxyl groups on a cyclohexyl
structure represented by a general formula (1).
##STR00002##
X is (a) one or more carboxyl groups, or (b) one or more carboxyl
groups and at least one selected from a hydrogen atom, chloro
group, bromo group, alkyl group, and cyclohexyl group. A position
of the X is not limited. A number of the X is one or more. The X
may have either one of the (a) and (b) alone, or a plurality of the
(a) and (b) in combination.
[0012] According to another aspect of the present invention, a
solder paste composition includes a solder alloy powder and a flux
for soldering. The flux for soldering includes a base resin, a
solvent, and an activating agent. The base resin contains a rosin.
An amount of the rosin to be incorporated is from 0% by weight to
30% by weight with respect to a total amount of the base resin. The
activating agent includes a compound having a plurality of carboxyl
groups on a cyclohexyl structure represented by a general formula
(1).
##STR00003##
X is (a) one or more carboxyl groups, or (b) one or more carboxyl
groups and at least one selected from a hydrogen atom, chloro
group, bromo group, alkyl group, and cyclohexyl group. The position
of the X is not limited. A number of the X is one or more. The X
may have either one of the (a) and (b) alone, or a plurality of the
(a) and (b) in combination.
DESCRIPTION OF THE EMBODIMENTS
[0013] A detailed description will hereinafter be given of an
embodiment of the flux for soldering and the solder paste
composition of the present disclosure. It goes without saying that
the present invention will not be limited to the embodiment.
Embodiment
1. A Flux for Soldering
(1) a Base Resin
<A Rosin>
[0014] A rosin used as a base resin in the embodiment includes, for
example, a rosin such as a tall oil rosin, gum rosin, and wood
rosin; a rosin derivative such as a hydrogenated rosin, polymerized
rosin, disproportionated rosin, acrylic acid modified rosin, and
maleic acid modified rosin; or the like.
[0015] The rosins mentioned above may be used alone or in
combination. In addition, the rosin usable in the flux for
soldering of the embodiment is not limited thereto.
[0016] The amount of the rosin to be incorporated is from 0% by
weight to 30% by weight with respect to a total amount of the base
resin. In other words, even when the rosin content is 0, a solder
paste composition in which the flux for soldering of the embodiment
is used may achieve a good reflow property.
<A Resin Other than the Rosin>
[0017] Into the base resin in the embodiment, a resin other than
the rosin may be incorporated, including, for example, an acrylic
resin, styrene-maleic acid resin, epoxy resin, urethane resin,
polyester resin, phenoxy resin, terpene resin, or the like.
[0018] The other resins mentioned above may be used alone or in
combination. In addition, the resin usable in the flux for
soldering of the embodiment is not limited thereto.
[0019] Particularly, an acrylic resin is preferably used as the
other resin mentioned above. Such an acrylic resin is obtained by
polymerizing a monomer alone or copolymerizing a plurality of types
of monomers, such as a carboxyl group-containing monomer such as
(meth)acrylic acid, itaconic acid, maleic acid, and crotonic acid;
and a monomer such as octyl(meth)acrylate, nonyl(meth)acrylate,
decyl(meth)acrylate, undecyl(meth)acrylate, dodecyl(meth)acrylate,
tridecyl(meth)acrylate, tetradecyl(meth)acrylate,
lauryl(meth)acrylate, stearyl(meth)acrylate, and an isoform
thereof, methyl(meth)acrylate, ethyl(meth)acrylate,
butyl(meth)acrylate, hexyl(meth)acrylate, propyl(meth)acrylate.
[0020] Among the acrylic resins mentioned above, particularly the
following resins are preferably used:
(i) (a) an acrylic resin obtained through a polymerization reaction
of a long-chain alkyl group-containing (meth)acrylic monomer; (ii)
an acrylic resin obtained by copolymerizing the monomer (a), and at
least one of (b) a (meth)acrylic acid and (c) (meth)acrylic monomer
other than the monomer (a).
[0021] The glass transition temperature (Tg) and acid value of the
acrylic resin mentioned above may be appropriately adjusted based
on the ratio or amount of the used monomer(s) to be incorporated,
the condition at polymerization or copolymerization, or the
like.
[0022] In addition, it is preferable that the amount of the base
resin to be incorporated be from 30% by weight to 60% by weight
with respect to a total amount of the flux for soldering.
(2) an Activating Agent
<A Compound Having a Plurality of Carboxyl Groups on a
Cyclohexyl Structure>
[0023] An activating agent used in the flux for soldering of the
embodiment includes a compound having a plurality of carboxyl
groups on a cyclohexyl structure represented by the general formula
(1):
##STR00004##
[0024] wherein the X is (a) one or more carboxyl groups, or (b) one
or more carboxyl groups and at least one selected from the group of
a hydrogen atom, chloro group, bromo group, alkyl group, cyclohexyl
group and the like,
[0025] the position of the X is not limited,
[0026] the number of the X is one or more, and
[0027] the X may have either one of the (a) and (b) alone, or a
plurality of the (a) and (b) in combination.
[0028] In general, when the rosin content in a flux for soldering
is small, the reflow property of a solder paste composition may be
disturbed. A common method for improving the reflow property
includes increasing the amount of the activating agent to be
incorporated.
[0029] A short-chain fatty acid such as adipic acid and succinic
acid, which is conventionally used as the activating agent, will be
volatilized or decomposed by heat in the event of the pre-heating
in the soldering step, even when the amount of the short-chain
fatty acid to be incorporated is increased. Accordingly, such a
solder paste composition is difficult to achieve an improving
effect on the reflow property, but rather may decrease the
resistance to crack in its flux residue.
[0030] On the other hand, in a case where a long-chain fatty acid
is used as the activating agent, in order to improve the reflow
property of a solder paste composition, an amount of the long-chain
fatty acid that will be sufficient to disturb the printability is
preferably incorporated. In addition, in this case, the resistance
to crack in its flux residue may be disturbed.
[0031] However, because the solder paste composition in which the
flux for soldering of the embodiment is used includes the compound
having a plurality of carboxyl groups on a cyclohexyl structure
represented by the general formula (1) as the activating agent, the
content by percentage of carboxyl groups is high and the volatility
is low at high temperature. Therefore, even when the rosin content
is low, the solder paste composition may achieve a good reflow
property without increasing the amount of the activating agent to
be incorporated.
[0032] The compound having a plurality of carboxyl groups on a
cyclohexyl structure may be any one represented by the general
formula (1). Such a compound includes, for example,
1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid,
hydrogenated trimellitic acid, and hydrogenated pyromellitic acid.
Among them, particularly 1,4-cyclohexanedicarboxylic acid,
hydrogenated trimellitic acid, and hydrogenated pyromellitic acid
are preferably used. These may be used alone or in combination.
[0033] It is preferable that the amount of the compound mentioned
above to be incorporated be of 0.5% by weight or more with respect
to a total amount of the flux for soldering.
<The Other Activating Agent>
[0034] As the activating agent in the flux for soldering of the
embodiment, the compound having a plurality of carboxyl groups on a
cyclohexyl structure may be used alone or in combination with the
other activating agent than the compound.
[0035] The other activating agent than the compound having a
plurality of carboxyl groups on a cyclohexyl structure includes,
for example, an amine salt (inorganic acid salt or organic acid
salt) such as a hydrohalide salt of an organic amine, organic acid,
organic acid salt, organic amine salt or the like. A specific
example includes a diphenylguanidine hydrobromate salt,
cyclohexylamine hydrobromate salt, diethyl amine salt, acid salt,
succinic acid, adipic acid, sebacic acid or the like. These may be
used alone or in combination. In addition, the activating agent
usable in the flux for soldering of the embodiment is not limited
thereto.
[0036] As to the amount of the other activating agent to be
incorporated, it is preferable that a total amount of the other
activating agent and the compound having a plurality of carboxyl
groups on a cyclohexyl structure be from 5% by weight to 15% by
weight with respect to a total amount of the flux for
soldering.
(3) A Solvent
[0037] A solvent used for a flux for soldering of the embodiment
includes, for example, isopropyl alcohol, ethanol, acetone,
toluene, xylene, ethyl acetate, ethylcellosolve, butylcellosolve,
glycol ether or the like. These may be used alone or in
combination. In addition, the solvent usable for the flux for
soldering of the embodiment is not limited thereto.
[0038] It is preferable that the amount of the solvent to be
incorporated be from 20% by weight to 50% by weight with respect to
a total amount of the flux for soldering.
(4) An Antioxidant
[0039] An antioxidant may be incorporated into the flux for
soldering of the embodiment for the purpose of suppressing the
oxidation of a solder alloy powder. The antioxidant includes, for
example, a hindered phenolic antioxidant, phenolic antioxidant,
bisphenolic antioxidant, polymer type antioxidant or the like.
Among them, particularly a hindered phenolic antioxidant is
preferably used. Moreover, these may be used alone or in
combination. In addition, the antioxidant usable in the flux for
soldering of the embodiment is not limited thereto.
[0040] The amount of the antioxidant to be incorporated is not
particularly limited. The general amount thereof to be incorporated
is from approximately from 0.5% by weight to 5% by weight with
respect to a total amount of the flux for soldering.
(5) A Thixotropic Agent
[0041] A thixotropic agent may be incorporated into the flux for
soldering of the embodiment for the purpose of adjusting the solder
paste composition so as to have a suitable viscosity for printing.
Such a thixotropic agent includes, for example, a hydrogenated
castor oil, fatty acid amides, hydroxy fatty acids or the like. In
addition, the thixotropic agent usable in the flux for soldering of
the embodiment is not limited thereto.
[0042] It is preferable that the amount of the thixotropic agent to
be incorporated be from 3% by weight to 15% by weight with respect
to a total amount of the flux for soldering.
(6) An Additive Agent
[0043] An additive agent such as a halogen, flatting agent and
antifoaming agent may be further added into the flux for soldering
of the embodiment. It is preferable that the amount of the additive
agent to be incorporated be of 10% by weight or less, or it is more
preferable that the amount thereof be of 5% by weight, with respect
to a total amount of the flux for soldering.
2. A Solder Alloy Powder
[0044] A solder alloy powder used in the solder paste composition
of the embodiment includes one combining two or more of, for
example, Sn, Ag, Cu, Bi, Zn, In, Ga, Sb, Au, Pd, Ge, Ni, Cr, Al, P,
In, Pb and the like. As the representative solder alloy powder, a
lead-free solder alloy powder such as Sn--Ag--Cu and Sn--Ag--Cu--In
is used, but a lead-containing solder alloy powder may also be
used.
[0045] It is preferable that the amount of the solder alloy powder
to be incorporated be of 65% by weight or more but 95% by weight or
less with respect to a total amount of the solder paste
composition. The more preferable amount thereof to be incorporated
is of 85% by weight or more but 93% by weight or less, or the
particularly preferable amount thereof to be incorporated is of 89%
by weight or more but 92% by weight or less.
[0046] The solder paste composition having an amount of the solder
alloy powder to be incorporated less than 65% by weight tends to
become difficult to form an enough solder joint at the time of
soldering. On the other hand, the solder paste composition having
an amount of the solder alloy powder to be incorporated more than
95% by weight has an insufficient flux for soldering as a binder,
with the result that the flux for soldering and the solder alloy
powder tend to become difficult to be mixed.
[0047] The solder paste composition of the embodiment is prepared
by mixing the flux for soldering mentioned above and the solder
alloy powder mentioned above using a well-known method.
Examples
[0048] A detailed description will hereinafter be given of the
embodiment of the present invention with reference to Examples and
Comparative Examples. It goes without saying that the present
invention will not be limited to these Examples.
Production of an Acrylic Resin
[0049] A solution 1 was prepared in which 40% by weight of a
compound represented by the general formula (2) and 60% by weight
of a compound represented by the general formula (3) were
mixed.
##STR00005##
[0050] In a 500 ml four neck flask equipped with an agitator,
recirculating pipe and nitrogen introducing pipe, 200 g of diethyl
hexyl glycol was placed and heated to 110.degree. C. Subsequently,
in the solution 1 (300 g in total), 0.2% by weight to 5% by weight
of an azoic radical initiator (dimethyl 2,2'-azobis(2-methyl
propionate), commercial name: V-601, made by Wako Pure Chemical
Industries, Ltd.) was added and dissolved. The resultant solution
was dropped over 1.5 hours, followed by stirring for 1 hour at
110.degree. C. Completion of the reaction gave an acrylic resin.
The acrylic resin had a weight-average molecular weight of 15,000,
and an acid value of 0 mgKOH/g.
Preparation of a Solder Paste
[0051] In accordance with the composition and formulation indicated
in Table 1, the respective ingredients were mixed and kneaded, and
then the respective fluxes for soldering according to Examples 1 to
4 and Comparative Examples 1 to 7 were prepared. Note that in Table
1, the unit of the numerical value relating to the composition is %
by weight, unless otherwise indicated.
[0052] Subsequently, 12% by weight of the respective fluxes for
soldering mentioned above were mixed with 88% by weight of a
Sn-3Ag-0.5Cu solder alloy powder, and then the respective solder
paste compositions according to Examples 1 to 4 and Comparative
Examples 1 to 7 were obtained.
TABLE-US-00001 TABLE 1 Comparative Comparative Example 1 Example 2
Example 3 Example 4 Example 5 Example 1 Example 2 Acrylic Resin
Acrylic resin 40 40 40 35 35 40 40 (Synthetic) Rosin KE-604 5 5 5
10 0 5 5 Compound Having Cyclohexanecarboxylic 5 Carboxyl Group On
acid Cyclohexyl 1,4- 5 10 Structure Cyclohexanedicarboxylic acid
H-TMA*2 5 0.5 Other Activating Succinic acid 5 Agent Adipic acid 5
5 SL-20 *3 Dimer acid Terephthalic acid Trimellitic acid
Thixotropic agent SLIPACKS ZHH*4 7 7 7 7 7 7 7 Antioxidant IRGANOX
245*5 1 1 1 1 1 1 1 Solvent 2-ethylhexy 42 42 42 46.5 42 42 42
diglycol Comparative Comparative Comparative Comparative
Comparative Example 3 Example 4 Example 5 Example 6 Example 7
Acrylic Resin Acrylic resin 40 40 40 40 (Synthetic) Rosin KE-604 5
5 5 5 40 Compound Having Cyclohexanecarboxylic 5 Carboxyl Group On
acid Cyclohexyl 1,4- Structure Cyclohexanedicarboxylic acid H-TMA*2
Other Activating Succinic acid Agent Adipic acid SL-20 *3 5 Dimer
acid 5 Terephthalic acid 5 Trimellitic acid 5 5 Thixotropic agent
SLIPACKS ZHH*4 7 7 7 7 7 Antioxidant IRGANOX 245*5 1 1 1 1 1
Solvent 2-ethylhexy 42 42 42 42 42 diglycol *1 Hydrogenated rosin
made by Arakawa Chemical Industries, Ltd. *2Hydrogenated
trimellitic acid anhydride made by Mitsubishi Gas Chemical Company,
Inc. *3 Eicosanedioic acid made by Okamura Oil Mill Co., Ltd.
*4Fatty acid amide made by Nippon Kasei Chemical Co., Ltd.
*5Hindered phenolic antioxidant made by BASF Japan Ltd.
[0053] The respective solder paste compositions according to
Examples 1 to 4 and Comparative Examples 1 to 7 were measured and
evaluated as follows. The results are indicated in Table 2.
<The Reflow Property (Solder Wettability)>
[0054] In accordance with the condition specified in JIS standard
Z3284 (1994), Annex 10, respective test pieces of the solder paste
compositions were prepared, and a test for the wetting effect was
done. Subsequently, the whole appearance of the respective test
pieces at the completion of the test was evaluated as follows.
[0055] Note that the respective test pieces prepared were exposed
to a pre-heating treatment with the use of a hot plate at
180.degree. C. for 60 seconds, and then molten in a solder bath at
270.degree. C.
[0056] .largecircle.: all of the parts coated with the solder paste
composition are in a wet state with a solder.
[0057] .DELTA.: almost all of the parts coated with the solder
paste composition are in a wet state with a solder (dewetting is
also included)
[0058] x: there is no appearance of the test piece wetted with a
solder, but one or more solder balls of a molten solder are on the
test piece (non-wetting).
<The Preservation Stability>
[0059] The respective solder paste compositions were stored at
30.degree. C. for 3 days, and then the viscosity thereof was
measured with the use of a viscometer (product name: PCU-205, made
by Malcom Co., Ltd.) and evaluated as follows.
[0060] .largecircle.: the rate of change of the viscosity with
respect to the initial value is .+-.30% or less
[0061] x: the rate of change of the viscosity with respect to the
initial value is beyond .+-.30%
<The Resistance to Crack in the Residue>
[0062] On a board on which a QFP (Quad Flat Package) pattern having
a pitch of 0.8 mm was present, the respective solder paste
compositions were printed with the use of a metal mask having the
same pattern and a thickness of 150 .mu.m. Within 10 minutes from
the completion of the printing, a reflow was performed to the
respective printed boards under an oxygen concentration of 4,000
ppm at a maximum temperature of 240.degree. C., with the use of a
reflow furnace (product name: TNP40-577PH, made by Tamura
Corporation). After the respective reflowed boards were left at
150.degree. C. for 200 hours, to these was applied a cool-heat
cycle load including 50 cycles, each one cycle of which is from
-40.degree. C. x 30 minutes to 125.degree. C. x 30 minutes, with
the result that respective test pieces were prepared. The state of
crack initiation in a soldered part of the QFP pattern on the
respective test pieces was visually observed and evaluated based on
the following criteria.
[0063] .largecircle.: the number of cracks connecting terminals of
QFP joint parts (96 in total) is less than 10.
[0064] x: the number of cracks connecting terminals of QFP joint
parts (96 in total) is 10 or more.
TABLE-US-00002 TABLE 2 Comparative Comparative Example 1 Example 2
Example 3 Example 4 Example 5 Example 1 Example 2 Wetting effect
Wettability to .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle. copper
Wettability to .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. X X brass Preservation stability
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. X X Resistance to crack in residue .largecircle.
.largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle. Comparative Comparative Comparative
Comparative Comparative Example 3 Example 4 Example 5 Example 6
Example 7 Wetting effect Wettability to X X X X .largecircle.
copper Wettability to X X X X .largecircle. brass Preservation
stability .largecircle. .largecircle. .largecircle. X .largecircle.
Resistance to crack in residue .largecircle. .largecircle.
.largecircle. .largecircle. X
[0065] From the above, as indicated in Examples, it is found that
the solder paste compositions of the Examples exhibit a good reflow
property and preservation stability, and have an excellent
resistance to crack in their flux residues, when the rosin content
is small, and even when the rosin content is 0.
[0066] When a short-chain organic acid which does not have a
cyclohexyl structure is used as the activating agent, as in the
case of Comparative Example 1 and Comparative Example 2, the
wettability to brass and the preservation stability are disturbed.
In addition, when a long-chain organic acid which does not have a
cyclohexyl structure is used as the activating agent, as in the
case of Comparative Example 3 and Comparative Example 4, the
wettability to copper and brass is disturbed. Furthermore, when an
aromatic carboxylic acid which does not have a cyclohexyl structure
is used as the activating agent, as in the case of Comparative
Example 5 and Comparative Example 6, the wettability to copper and
brass, and the preservation stability are disturbed. Moreover, when
the rosin content is large, as in the case of Comparative Example
7, the resistance to crack in the flux residue is disturbed.
[0067] Accordingly, because the solder paste compositions of the
Examples are excellent in the reflow property and the preservation
stability, as well as excellent in the resistance to crack in the
flux residue, they may be suitably used for a board that will be
used under an environment where a particularly high reliability is
required.
[0068] The embodiment of the present invention provides a flux for
soldering capable of, even with the rosin content reduced,
exhibiting a good reflow property, good preservation stability, and
inhibiting effect on the crack initiation and crack development in
the flux residue under a severe cool-heat cycle environment over a
long period of time.
[0069] In addition, the embodiment of the present invention
provides a solder paste composition, in which is used a flux for
soldering capable of exhibiting a good reflow property, good
preservation stability, and inhibiting effect on the crack
initiation and crack development in the flux residue under a severe
cool-heat cycle environment over a long period of time.
[0070] The embodiment of the present invention is characterized by
being composed as follows in order to obtain the above mentioned
benefits.
[0071] (1) A flux for soldering of the embodiment of the present
invention includes a base resin containing a rosin, the amount of
the rosin to be incorporated being from 0% by weight to 30% by
weight with respect to a total amount of the base resin, an
activating agent including a compound having a plurality of
carboxyl groups on a cyclohexyl structure represented by the
general formula (1)
##STR00006##
[0072] wherein the X is (a) one or more carboxyl groups, or (b) one
or more carboxyl groups and at least one selected from the group of
a hydrogen atom, chloro group, bromo group, alkyl group, cyclohexyl
group and the like,
[0073] one or more positions of the X are present,
[0074] the number of the X is either one or more, and
[0075] the X may have either one of the (a) and (b) alone, or a
plurality of the (a) and (b) in combination, and
[0076] a solvent.
[0077] (2) In the composition of the item (1), the amount of the
compound to be incorporated having a plurality of carboxyl groups
on a cyclohexyl structure represented by the general formula (1) is
of 0.5% by weight or more with respect to a total amount of the
flux for soldering.
[0078] (3) In the composition of the item (1) or (2), the compound
having a plurality of carboxyl groups on a cyclohexyl structure
represented by the general formula (1) is at least one selected
from the group of cyclohexanedicarboxylic acid, hydrogenated
trimellitic acid, and hydrogenated pyromellitic acid.
[0079] (4) In the composition of any one of the items (1) to (3),
the flux for soldering of the embodiment of the present invention
has the amount of the base resin to be incorporated from 30% by
weight to 60% by weight with respect to a total amount of the flux
for soldering, the amount of the activating agent to be
incorporated from 5% by weight to 15% by weight with respect to a
total amount of the flux for soldering, the amount of the solvent
to be incorporated from 20% by weight to 50% by weight with respect
to a total amount of the flux for soldering, the amount of the
rosin to be incorporated from 0% by weight to 30% by weight with
respect to a total amount of the base resin, and the amount of the
compound to be incorporated having a plurality of carboxyl groups
on a cyclohexyl structure represented by the general formula (1) of
0.5% by weight or more with respect to a total amount of the flux
for soldering.
[0080] (5) A solder paste composition of an aspect of the
embodiment of the present invention includes the flux for soldering
according to any one of the items (1) to (4), and a solder alloy
powder.
[0081] In accordance with the embodiment of the present invention,
even when the flux for soldering has a reduced rosin content, it is
possible to exhibit a good reflow property and good preservation
stability, as well as to inhibit the crack initiation and
development in the flux residue under a severe cool-heat cycle
environment over a long period of time.
[0082] Obviously, numerous modifications and variations of the
present invention are possible in light of the above teachings. It
is therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *